Having a boiler installed can be overwhelming since there are many steps to be taken. Among these steps is choosing the boiler type. Numerous homeowners prefer combination boilers over the others due to their efficiency. Why don’t you make things easier for yourself by going for a combi boiler? They are currently the most sought-for boiler type in the UK.

These boilers can provide immediate hot water even without storage tanks. Because of their self-sustainability, combi boilers make great options for properties with limited spaces. For those who are uncertain about what combi boiler size to go for, this guide will provide you several factors that you need to consider to make deciding easier.

Why Your Combi Boiler’s Size Matters

Aside from keeping your home comfortable to live in, the ideal combi boiler should also keep your energy bills as low as possible. Choosing a combi-boiler variant too large for your property will unnecessarily increase your costs on electricity and gas. Due to this, the act of ensuring that your combi boiler has the right size and output rating becomes very important.

Another thing you need to consider is the boiler’s output rating, which is measured in kilowatts (kW). Opting for a combi boiler with an overly-low output rating will leave your house cold and uncomfortable. On the other hand, installing a boiler with a rating that is too high will waste fuel and result in higher energy bills. These two factors play a vital role when it comes to getting the proper combi-boiler variant.

How to Determine Your Ideal Combi Boiler Size

Most of the time, combi boilers come in bigger sizes than regular and system boilers since they produce hot water for heating and domestic use. Because of this characteristic, these boilers also have two output ratings – domestic hot water (DHW) output and central heating (CH) output.

Combi Boiler Sizing Guide

Using your property’s number of radiators as a guide, you can determine the right combi boiler for you. Here is a combi boiler sizing guide you can follow:

  • Less than 10 radiators – combi boiler with 24kW to 27kW CH output
  • 10 to 15 radiators – combi boiler with 28kW to 34kW CH output
  • 15 to 20 radiators – combi boiler with 35kW to 42kW CH output

Should You Switch to a Combi Boiler?

Combi boilers are new additions to the home heating industry, but they’ve quickly gained recognition over the years. Their sudden popularity is not surprising since these boilers don’t need cylinders and tanks to work, saving lots of valuable space. These are some of the many benefits of switching to a combi boiler:

  • Immediate production of hot water is possible (waiting for the cylinder to fill up is not required)
  • You won’t be needing additional components (which can be costly)
  • A combi boiler can reside in a kitchen cupboard where it is not visible


Going for a combi boiler that’s either too big or too small would adversely affect your home’s comfort quality. Thankfully, finding the ideal combi-boiler size for your property is easily achievable by following the sizing guide provided above.

Whether you are hesitant to make the switch or you’re dealing with a combi boiler installation for the first time, you won’t go wrong in choosing this boiler type. The space-saving traits and cost-efficiency that comes with it will surely be beneficial for most homeowners.